Our research group has demonstrated that NMR imaging can be used to determine quantitatively lung water and its distribution, in contrast with the common belief that NMR is unsuitable for the study of lung. The NMR relaxation mechanisms of lung will be investigated using a multidisciplinary approach which includes mathematical and physical models as well as biological experiments with isolated and intact mammalian lung. Recent observations by the Principal Investigator and his collaborators of an internal source of inhomogeneous line broadenign in inflated (but not deflated) lung has led to a mechanism based upon air/water interfaces which is unique to lung tissue. These observations have resulted in our developing a new high-contrast NMR imaging technique in which only aerated portions of the lung are displayed. The line broadening of lung will be calculated for various geometrical models consisting of air bubbles in water. Our preliminary work with these models shows excellent agreement between our calculated and experimentally measured line broadening. The proposed experiments with models and lungs will define the details and quantify the contribution of lung inflation and air/water interfaces, utilizing gravimetric and morphometric techniques for reference. It is proposed to use these NMR features to develop new noninvasive NMR methods for determining regional lung density and alveolar size. In addition to the above, experiments with modesl and lungs will explore the as yet undefined relationship between lung inflation and spin-lattice relaxation (T1). A sensitive line technique will be employed for studies in rats. These studies will provide the basis for future experiments on larger animals with larger alveolar diameters (dogs, cats) using a 30 cm diameter superconducting system (currently on order) and eventually on humans using whole-body systems (on order for our affiliated hospitals in Salt Lake City).